Equipment for making elongated shapes from polyamides



I 1956 w. J. DAVIS ETAL EQUIPMENT FOR MAKING ELONGATED SHAPES FROM POLYAMIDES Filed May 19, 1952 ll ull III Ihl 2 Sheets-Sheet l Feb. 28, 1956 Filed May 19, 1952 w. J. DAVIS ET AL 2,736,057

EQUIPMENT FOR MAKING ELONGATED SHAPES FROM POLYAMIDES 2 Sheets-Sheet 2 United States Patent C) EQUIPMENT FOR MAKING ELONGATED SHAPES FROM POLYAMIDES William J. Davis and Robert B. Koch, Reading, Pa., assignors to Polymer Corporation, Reading, Pa., a corporation of Pennsylvania Application May 19, 1952, Serial No. 288,598 12 Claims. (CI. 18-12) This invention relates to the production of elongated shapes such as rods or tubing from certain high polymers, especially the synthetic linear polyamides which are known to the trade as nylon.

The equipment of the invention is of especial use in the formation of elongated shapes from the so-called high melting polyamides, examples of which are polyhexamethylene adipamide and polyhexamethylene sebacamide.

The invention is concerned with improvements in the general type of equipment providing for continuous for mation of elongated shapes, as disclosed for example in the copending application of Louis L. Stott, Serial No. 215,339, filed March 13, 1951, issued October 4, 1955, as Patent No. 2,719,330 and assigned to the assignee of the present application.

In general in the type of operation here involved, an elongated forming tube is employed, the tube being open ended. A feeder mechanism introduces molten polyamide into the entrance end of the forming tube to be advanced therethrough and delivered from the opposite end of the forming tube, and during passage of the material through the tube the material is cooled and solidified so that the elongated shape is delivered from the discharge end of the tube in solidified condition.

Such an operation, as disclosed in the copending application above identified, requires effecting solidification of the polyamide under a relatively high pressure, for instance, upwards of about 200 p. s. i., and most advantageously several times that minimum figure. This pressure is developed in part as a result of the contact of the material with the interior surface of the forming tube, the feeder mechanism reacting, so ,to speak, against this frictional engagement of the material with thetube wall in developing back pressure. (Additional back pressure may be developed by use of a braking mechanism engaging the formed rod beyond the delivery end of the forming tube, as described hereinafter.)

The zone or region of high pressure frictional engagement of the material with the inside surface of the forming tube is located toward the entrance end of the tube where the initial solidification occurs. As the material progressively solidifies radially inwardly from the tube wall toward the center or core of the piece being formed, the solidifying polyamide shrinks away from the tube wall.

For several reasons including the necessity for employing relativelyhigh pressure, it is advantageous to utilize a forming tube made of metal, for instance, a steel tube. Howeventhe frictional characteristics of such steel tube, even when highly polished, are such that it is difiicult to maintain uniform feed of the-material through the tube and uniform pressure in the entrance end, in consequence of which the physical characteristics of the shape being formed are not always uniform lengthwise thereof.

One of the principal objects of the invention is to provide a forming tube having an interior surface comprising a material having-an unusually low coefiicient of friction. We have found polytetrafluoroethylene is par- 2 ticularly effective for this purpose, especially when applied to the internal surface of the tube in the form of a thin coating bonded to the metal of the tube. The use of a polytetrafluoroethylene coating bonded to the tube Wall is of great advantage for a number of reasons, including the fact that the thin coating does not appreciably reduce the rate of heat transfer radially outwardly through the wall of the forming tube, and further because such a coating, in effect, is structurally a part of the tube itself rather than a separate element capable of movement with relation to the surrounding metal tube.

While we pefer to employ a thin coating, as above described, a wear problem is thereby introduced, and ac cording to another feature of the invention provision is made for compensating for wear of the coating.

In considering this wear problem, it is mentioned that the zone of high pressure frictional engagement of the material with the internal wall of the forming tube is of relatively short length axially of the tube and lies toward the entrance end of the tube. With this in mind, according to the invention, a cooling jacket surrounds the tube in the region of its entrance end, and this jacket is mounted for shifting movement lengthwise of the forming tube. In use the cooling jacket is progressively shifted from an initial position very close to the entrance end of the forming tube toward the discharge end of the forming tube as the polytetrailuoroethylene coating wears away as a result of the friction of the material solidifying against the tube wall.

The invention contemplates the employment of other temperature regulating jackets along the forming tube, and the mounting of all of the jackets for concurrent shifting movement when compensating for wear of the polytetrafluoroethylene coating, to thereby maintain the several jackets in their proper relative positions.

How the foregoing objects and advantages are attained will appear more fully from the following description, referring to the accompanying drawings, in which Figure 1 is a side outline view of a general assembly of equipment for continuously forming elongated shapes from polyamides and including the features of the present invention, certain parts being shown in vertical section for clarity;

Figure 2 is an enlarged side view of certain parts shown in Figure 1, illustrating particularly the adjustable mounting for certain of the jackets associated with the forming tube, some parts also being here shown in vertical section for clarity; and

Figure 3 is a longitudinal sectional view through a forming tube constructed according to the present invention and further including a centrally disposed mandrel providing for the formation of tubular shapes.

In the general assembly of the equipment as appears in Figure 1, a screw feed device 4 is shown as mounted on a standard 5, the feed screw 6 of this device being driven from a motor 7 through gearing 8. The details of the screw drive need not be considered herein since they form no part of the present invention per se. The material to be used is fed to the screw feed device through a funnel 9, usually in flake or granular form, and this material enters the barrel in the feed device. The barrel is surrounded by a heating jacket 10, and the action of the screw 6 and the heating jacket melts and advances a stream of molten material to the entrance end of the forming tube.

As best seen in Figure 2, the delivery end of the feeder barrel communicates with a chamber 11 provided in the housing 12 which is arranged at the delivery end of the feeder mechanism. A pressure responsive device 13 may be arranged in chamber 11 and provided with a fluid pressure connection 14 extended to control mechanism (not shown) for regulating the feed device. This pressure responsive control need not be described in detail herein, since it forms no part of the present invention per se. heating element surrounds the housing 12 in order to maintain the material in the chamber .lll in molten condition.

The molten material is delivered from the chamber 11 to the interior of the elongated forming tube 16. The material in the entrance end of the forming tube is maintained in molten condition by means of a jacket 17 which may be heated by element 18.

As the material passes through the forming tube iii, it is progressively solidified radially inwardly and thus forms a solidified rod indicated at 19.

As seen in Figure I, feed controlling rolls lid-2t) may be arranged beyond the delivery end of the forming tube. These rolls may be driven at a regulated speed to reduce irregularity in the rate of feed of the rod. Similarly, a friction clamp brake mechanism 2?. may be associated with the rod just beyond the end of the delivery tube in order to apply a force tending to retard the advancement of the formed rod.

According to the invention, the forming tube 16 is preferably made of metal and is lined with a coating of polytetrafiuoroethylene as shown at 22 in Figure 2. This coating is illustrated exaggerated as to thickness.

In providing a coated tube for this purpose, one construction and method of preparing the tube involves the use of a stainless steel tube, on the interior surface of which an aqueous suspensoid of polytetratluoroethylene, chromic acid, phosphoric acid and a dispersing agent is applied. The coating is dried and baked to fuse the polytetrafluoroethylene, a temperature in the range of about 675 F. to about 750 F. being appropriate for this purpose.

The foregoing operation provides a coating which is effectively bonded to the inner surface of the tube. One or more additional layers of polytetrafiuoroethylene may be applied, these preferably being formed from a simple aqueous dispersion of the polytetrafiuoroethylene, with a dispersing agent. Several layers of such coating may be applied.

The foregoing operation provides a highly effective forming tube for the purpose of continuously forming elongated shapes from polyamides. The coating itself is directly bonded to the metal of the tube; it is thin, and therefore does not appreciably retard the rate of heat transfer radially outwardly through the tube wall. The coating has an exceptionally low coefficient of friction, almost soap-like in texture; while at the same time being composed of polytetrafiuorocthylene, the coating has a softening point well above that encountered in the handling of any of the polyamides. To illustrate, one of the highest melting polyamides is the polyhexamethylene adipamide, melting at about 505 F, whereas the polytetrafiuoroethylene coating does not soften appreciably even at temperatures as high as 620 P.

However, as hereinabove mentioned, the relatively thin coating is subject to wear in the region of initial solidification of the polyamide in the forming tube. This initial solidification region is surrounded by a cooling jacket 23, through which a cooling liquid may be circulated as by means of inlet and outlet pipes 24, 25.

The jacket 23 is slidable along the forming tube and is mounted by means of a bracket 26 which is fixed to a rod 27, slidably arranged in fixed supports 28 and 29.

With the arrangement just described, shifting movement of the rod 27 will shift the jacket 23 lengthwise of the forming tube 16.

According to the invention, other temperature regulating jackets are also associated with the forming tube 16. These include a reheater jacket 36 having a heating element 31 located just beyond the initial cooling jacket 23, and one or more cooling jackets 32, all of which are also slidable along the forming tube 16 and all of which are arranged to be fixed to the rod 27, as by brackets 33 and 34. Each of the jackets 32 is provided with connections for the circulation of a heat transfer fluid therethrough, as indicated at 35.

The several cooling jackets and the reheating jacket may be made relatively adjustable by shifting the relative location of the mounting brackets with respect to each other and fixing them in such adjusted positions on the rod 27.

It will be understood that differences in heat transfer between the jackets and the forming tube are required to meet different operating conditions, for instance, differences in the diameter of the rod or other pieces being formed, differences in the rate of feed, differences in the polyamide being used, etc.

In a typical case, for instance in the formation of a solid rod from polyhexamethylene adipamide, the first cooling jacket 23 will serve to initially and sharply chill the outer layers of the material as it is initially solidifying. Thereafter, the reheater jacket 30 will serve to prevent unduly rapid continuance of chilling, and may even actually reintroduce a portion of the heat lost in the initial chilling effected by the jacket 23. The jackets 32 will serve to provide a controlled but relatively low rate of cooling, for which purpose these jackets are made of relatively great length as compared with the length of jackets 23 and 30. Moreover, the sectionalizing of the jackets 32 and the provision of separate connections for the passage of heat transfer medium therethrough provides for the establishment of a different temperature within each of the jackets 32. a

In a typical case, the temperatures of jackets 32 would progressively decrease from the first one to the last. The slow cooling is of advantage, especially with certain of the polyamides, notably the high melting polyamides, since this slow cooling acts in the general manner of an annealing operation thereby eliminating strain in the piece being formed.

After a certain quantity of material has been passed through the forming tube, the coating, especially in the region of the jacket 23, tends to wear away, and at such time the entire assembly of jackets is shifted somewhat along the length of the forming tube toward the discharge end thereof. For this purpose, an adjustable mechanism is provided including a screw 36, one end of which is rotatively but axially fixed with relation to a fixed frame part 37. The screw passes through a complementary threaded nut 38 which is fixed in a bracket 39, which, may for convenience, constitute a part of one of the brackets 34 for one of the jackets 32. The nut 38 is thus, in effect, fixed with relation to the rod 27 so that rotation of the screw 36 will advance all of the jackets fastened to the rod 27 concurrently.

When wear of the polytetrafluoroethylene coating of the forming tube has taken place and the rod 27 has been shifted to a new position, the point at which initial solidification of the rod occurs is likewise shifted toward the discharge end of the forming tube, and thereby the point of initial solidfication is brought to a region of the polytetrafluoroethylene coating which is not appreciably worn. If desired an additional heater jacket may be placed around the forming tube just beyond the jacket 17 when the cooling jackets are shifted.

In the description above, reference is madeto Fig'urm l and 2 in which the equipment is adapted to a production of solid rod stock. In contrast in Figure 3, there is shown an arrangement for producing a tubular shape. In general, the arrangement of parts when producing tubing is similar to that when producing rod stock, except that a mandrel 40 is arranged centrally within the forming tube 16.

In the practice of the invention, it is preferred to coat the exterior surface of the mandrel with polytetrafluoroethylene in the same manner as described above for coating-of the interior surface of the tube 16. Such a coating appears at 41 in Figure 3. be produced.

The end of the mandrel 40 adjacent to the feeding device 4 may be threaded into a boss locate. centrally of the mounting part 43, holes being provided around the mandrel so as to deliver the molten material from the chamber 11 in the housing 12 to the annular passage lying between the forming tube 16 and the mandrel 40.

It will be understood that in the arrangement of Figure 3 other mechanisms will be associated with the forming tube, especially the heat transfer jackets fully described in connection with Figures 1 and 2.

We claim:

1. Equipment for making elongated shapes from synthetic linear polyamides comprising an open-ended forming tube, a feeder for delivering molten polyamide into the entrance end of the forming tube to be solidified therein and discharged in solidified form from the opposite end of the forming tube, the tube having a lining of polytetrafluorethylene in the form of a thin coating bonded to the internal surface of the tube, and a temperature regulating element for the tube arranged in heat exchange relation to the exterior of the forming tube and mounted for shifting movement lengthwise of the tube.

2. Equipment of the character described comprising a forming tube having inlet and discharge openings toward opposite ends providing for the passage through the tube of material to be formed into elongated shapes, the tube having a thin lining of polytetrafluoroethylene, and a heat transfer jacket surrounding a portion of the tube toward its inlet end and mounted for shifting movement lengthwise of the tube.

3. Equipment for forming elongated shapes from synthetic linear polyamides comprising a forming tube having a thin internal coating of polytetrafiuoroethylene, mechanism for feeding molten polyamide into one end of the forming tube to be solidified therein and delivered from the other end in solidified form, and temperature control mechanism for the forming tube comprising a cooling jacket surrounding a portion of the tube toward its entrance end, the cooling jacket being shiftable lengthwise of the forming tube.

4. A construction according to claim 3 in which the temperature control mechanism further includes a reheating jacket surrounding the forming tube in a position between the cooling jacket and the delivery end of the tube.

5. A construction according to claim 4 in which the reheating jacket is shiftable along the forming tube.

6. A construction according to claim 5 and further including movable mounting means for the cooling and reheating jackets providing for concurrent shifting movements thereof.

7. A construction according to claim 4 and further including an annealing jacket surrounding the forming tube in a position between the reheating jacket and the delivery end of the tube.

8. A construction according to claim 7 in which all In this way, a tube 42 may three jackets are mounted for conjoint shifting move ments.

9. In the art of forming elongated shapes from synthetic linear polyamides, the method which comprises continuously melting the polyamide and delivering a stream of molten polyamide into the entrance end of an elongated forming tube having an open discharge end and having a lining of polytetrafiuoroethylene in the form of a thin coating bonded to the internal surface of the tube, advancing the polyamide through the tube, and cooling the polyamide during the advance thereof through the tube, the rate of cooling being sufficient to eflfect solidification of the polyamide throughout at least a major portion of the cross section thereof prior to delivery of the shape from the discharge end of the tube, the cooling action being initiated at a point which is shiftable along the length of the tube and the point of initiation of the cooling being progressively shifted during the effective life of the coating in a direction from the entrance end of the forming tube toward the discharge end thereof.

10. In the art of forming elongated shapes from synthetic linear polyamides, the method which comprises melting the polyamide and delivering a stream of molten polyamide into the entrance end of an elongated forming tube having an open discharge end, advancing the polyamide through the tube, initially cooling the polyamide during the advance thereof through the tube, reheating the polyamide during the advance thereof through the tube beyond the region of said initial cooling, and thereafter resuming the cooling of the polyamide during the advance thereof at a rate sufficient to effect solidification throughout at least a major portion of the cross-section thereof prior to delivery of the shape from the discharge end of the tube.

11. Equipment of the character described comprising a forming tube having inlet and discharge openings toward opposite ends providing for the passage through the tube of material to be formed into elongated shapes, the tube having a thin lining of polytetrafluorethylene, and heat transfer means associated with the tube and being mounted for shifting movement lengthwise of the tube.

12. A construction according to claim 11 in which the heat transfer means comprises cooling means associated with a portion of the tube toward its inlet end and being shiftable toward the discharge end of the tube.

References Qited in the file of this patent UNITED STATES PATENTS 

1. EQUIPMENT FOR MAKING ELONGATED SHAPES FROM SYNTHETIC LINEAR POLYAMIDES COMPRISING AN OPEN-ENDED FORMING TUBE, A FEEDER FOR DELIVERING MOLTEN POLYAMIDE INTO THE ENTRANCE END OF THE FORMING TUBE TO BE SOLIDIFIED THEREIN AND DISCHARGED IN SOLIDIFIED FORM FROM THE OPPOSITE END OF THE FORMING TUBE, THE TUBE HAVING A LINING OF POLYTETRAFLUORETHYLENE IN THE FORM OF A THIN COATING BONDED TO THE INTERNAL SURFACE OF THE TUBE, AND A TEMPERATURE REGULATION ELEMENT FOR THE TUBE ARRANGED IN HEAT EXCHANGE RELATION TO THE EXTERIOR OF THE FORMING TUBE AND MOUNTED FOR SHIFTING MOVEMENT LENGTHWISE OF THE TUBE. 